It is notable feature of the Old Testament that several accounts or passages occur more than once, often in similar but not identical fashion. Such repetitions have o en been a key feature leading to source-critical analyses of Old Testament texts, but several different types of examples of repetition are discussed in order to demonstrate that there is a bigger question to hand: why should the Old Testament canon be so marked by repetitions of material large and small? It is suggested that such repetition is not an unforeseen by-product of the editing and collation process, nor is it simply an editorial desire to include all tried and tested texts regardless of overlap. Rather repetition serves a theological function, which comes into focus when we consider Old Testament texts as a form of testimony. In the light of Deuteronomy 19:15 and questions of trustworthy testimony, it is suggested that textual repetition in the Old Testament serves to foreground a claim to the nature of these texts as reliable witness to the God of Israel. Some hermeneutical implications are explored briefly.